It says quite plainly that states should be able to field well regulated militias,

You clearly forget that they extended that right to artillery as well. You were just as legally entitled to own a field cannon loaded with grapeshot as you were a musket. In point of fact, wealthy people that owned ships could and did outfit their ships with cannon either to be privateers under a letter of marque, or to fight off pirates and the privateers of other countries.

But even at that, at the time when the constitution was written, muzzle-loaded firearms were the pinnacle of war-time weaponry. Bayonet charges were common, and swords still saw extensive use in pitched battles. Not only that, but people were legally obligated to own militarily-suitable arms, and they were expected to train on their own. The concept of having a brace of pistols comes from this era; while they didn’t have repeating rifles, they did have pepperbox pistols that could fire multiple times before being reloaded. So this idea that it was not the intent that the people should have access to militarily-suitable weapons simply isn’t borne out by an understanding of history.